This invention relates to engine control systems in general and more particularly to determining barometric pressure using a manifold pressure sensor in an engine control system for an internal combustion engine.
Barometric pressure, the force per unit area due to the weight of the atmosphere, can be measured in a variety of ways. Currently, in automotive applications, the barometric pressure can be measured using a barometric pressure sensor mountable on any suitable place on the vehicle where it sees true atmospheric pressure. Such a sensor generates an output signal indicative of the atmospheric pressure. The barometric pressure reading is then used for a number of automobile controls. For example, barometric pressure is used for fuel management, exhaust gas recirculation, spark timing, shift control, idle speed compensation and coast-down throttle angles. However, barometric pressure sensors can be costly and it is always desirable, particularly in automotive applications, to minimize costs.
It is well known in automotive engine control systems to measure the manifold absolute pressure (MAP) using a MAP sensor. The manifold absolute pressure value is measured in automobiles because it is necessary for fuel delivery accuracy. The MAP supplies information on how much air is ingested during each cylinder intake stroke and this information is then used in base fuel calculations to determine how much fuel is needed for each cylinder.
It is also well known in the industry that at certain engine conditions such as wide open throttle (WOT), when the engine is keyed on and when the ignition is off, MAP is substantially equal to barometric pressure. Some prior systems have used this fact to determine barometric pressure at those particular engine conditions by using the manifold absolute pressure sensor rather than a separate barometric pressure sensor. However, these systems are ineffective for updating barometric pressure under certain vehicle operating conditions such as a long uphill climb. It would be desirable, then, to devise a method for using the manifold absolute pressure sensor to determine barometric pressure at all other engine conditions, including part throttle.